Aromatic polyesters obtained directly from hydroxybenzoic acids by hexachlorocyclotriphosphatriazene (PNC) in pyridine

Polyaryl esters of moderate molecular weights were prepared by the direct polycondensation reaction of hydroxybenzoic acids and its derivatives with hexachlorocyclotriphosphatriazene (also known as phosphonitrilic chloride trimer, PNC) as a condensing agent in pyridine. Copolymerization of p-hydroxybenzoic acid with several hydroxybenzic acid derivatives was carried out to improve the processability of the polymer of p-hydroxybenzoic acid, which yields fusible and soluble copolymers of high inherent viscosities. Polymer solubility and thermal behavior were examined.     

Ionic salt permeabilities and membrane potentials of asymmetric polypeptide membrane

Asymmetric membrane potentials and transport properties of polypeptide membrane consisting of two layers with poly(L-glutamic acid) and poly (γ-methylL-glutamate) were studied in the pH range of 2 to 6 at 25 °C. Under the condition adopted, the poly (L-glutamic acid) layer of the membrane underwentα helix to coil transition which was confirmed by ATR-IR measurements. The membrane potentials of the asymmetric membrane between two identical solutions of KCl,Δψ _asym, which is called asymmetric potential, were observed.Δψ _asym values were effected by the structural transition of poly (L-glutamic acid) layer. As a result, the effective charge density of the membrane, which was derived by the asymmetric membrane potential measurements, had a maximum at the transition region of pH=4.8. On the other hand, the permeation coefficient of KCl,P _i, was higher in the direction from poly (L-glutamic acid) side to poly (γ-methylL-glutamate) side, “G →M direction”, than in the oppositeM →G direction. Furthermore,P _i inG →M direction was dependent on the solution pH, that is,P _i decreased when pH was increased to 4.8 and increased on further increasing of pH These membrane behaviors were described in terms of the competition between structural transition and variation of fixed charge density owing to the helix to coil transition of the asymmetric polypeptide membrane.     

Facile radical trifluoromethylation of lithium enolates

[reaction: see text] Highly basic lithium enolates are shown to be applicable to radical trifluoromethylation. The reaction is extremely fast, and the minimum reaction time is approximately 1 s.     

Collision-energy-resolved Penning ionization electron spectroscopy of p-benzoquinone: study of electronic structure and anisotropic interaction with He(*)(2 (3)S) metastable atoms

Collision energy dependence of partial ionization cross sections (CEDPICS) of p-benzoquinone with He(*)(2 (3)S) metastable atoms indicates that interaction potentials between p-benzoquinone and He(*)(2 (3)S) are highly anisotropic in the studied collision energy range (100-250 meV). Attractive interactions were found around the C==O groups for in-plane and out-of-plane directions, while repulsive interactions were found around CH bonds and the benzenoid ring. Assignment of the first four ionic states of p-benzoquinone and an analogous methyl-substituted compound was examined with CEDPICS and anisotropic distributions of the corresponding two nonbonding oxygen orbitals (n(O) (+),n(O) (-)) and two pi(CC) orbitals (pi(CC) (+),pi(CC) (-)). An extra band that shows negative CEDPICS was observed at ca. 7.2 eV in Penning ionization electron spectrum.     

1,4‐Addition polymerization of 1,4‐bis(4‐benzylpyridinium)butadiyne triflate in a dipolar aprotic solvent

1,4‐Bis(4‐benzylpyridinium)butadiyne triflate was aggregated in dimethylformamide and spontaneously converted into the 1,4‐addition type of polydiacetylene. The polymerization took place in a dipolar aprotic solvent with a large dielectric constant that could enhance the aggregation of the ionic diacetylene salt through the electrostatic interaction. The molecular weight of the diacetylene was leveled off after 30 h at 80 °C to reach 1.5 × 10⁴ (number‐average molecular weight) that consisted of the 1,4‐addition type of polydiacetylene similar to polydiacetylenes obtained in the conventional solid‐state polymerization. Electron spin resonance spectra revealed that diradicals were generated at the earlier state aggregation to give rise to a solution polymerization. The UV spectra also suggested the presence of the activated aggregation associated with the polymerization as well as the eximer emission spectra. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3534–3541, 2002     

Studies on penem and carbapenem. I. Syntheses and oral absorption of ester-type prodrugs of sodium (5R,6S)-2-(2-fluoroethylthio)-6-[(1R)-1-hydroxyethyl]penem-3-c arboxylat e

Acyloxyalkyl esters (2a-d), alkyloxycarbonyloxyalkyl esters (2e-g) and (5-methyl-2-oxo-1,3-dioxol-4-yl)methyl ester (2h) of (5R,6S)-2-(2-fluoroethylthio)-6-[(1R)-1-hydroxyethyl]penem-3- carboxylic acid (1) were synthesized. Enhanced oral absorption was observed in mice reflecting increased lipophilicity, compared with the parent 1 itself. Among them, the ester 2h showed a prolonged plasma level and a large area under the blood concentration-time curve (AUC) in rats. These ester-type prodrugs of penem 1 in phosphate buffer (pH 6.86) were much more stable than those of cephalosporins which easily degraded via isomerization to delta 2 cephalosporins.     

Photoelectron and penning ionization electron spectroscopic investigation of trimethylsilyl- and t-butyl-thiophenes

Penning ionization electron spectroscopy and CNDO/S calculations have been successfully applied to the analyses of the UV photoelectron spectra of 2- and 2,5-bistrimethylsilylthiophene and 2-t-butylthiophene. The relative intensities of the π type bands are greatly enhanced in the Penning spectra compared with those of the UV photoelectron spectra.     

Thermal behavior of ternary Sm2Fe17Nx magnets

The Mössbauer spectra of Sm₂Fe₁₇N_x, prepared by the nitrogenation of Sm₂Fe₁₇ powders in an ammonia and hydrogen atmosphere, were observed at elevated temperatures to shed light on the thermal behavior of nitrogen in the compounds Sm₂Fe₁₇N_x. It was found that there were large differences in thermal behavior between the starting Sm₂Fe₁₇, crystalline Sm₂Fe₁₇N_x (x≈1.7) and amorphous Sm₂Fe₁₇N_x(x～7). The thermal decomposition behavior of Sm₂Fe₁₇N_3.2, developed as one of the most promising hard magnetic materials, was found to be different under different atmospheres.     

Total synthesis of (+/-)-stemodinone via an efficient ring-exchange strategy

A total synthesis of (+/-)-stemodinone, a tetracyclic stemodane diterpene, from the known tricyclic methyl olefin 11 is described. The key steps involve an efficient ring-exchange reaction and palladium(0)-catalyzed lactone migration. The ring-exchange strategy for controlling the stereochemistry was based on an initial Diels-Alder reaction to form a new ring followed by cleavage of the original ring. Cleavage of the original ring of the Diels-Alder adduct 9 was achieved by an initial regio- and chemoselective Baeyer-Villiger oxidation followed by the Pd(0)-catalyzed lactone-migration reaction reported by us.